Organic carbonates are important intermediates in the chemical field, and can be used as reagents in methylation and carbomethoxylation reactions for the preparation of phenol ethers, quaternary salts of ammonium, ureas, urethanes, isocyanates and polycarbonates. These wide applications constitute a great need for the commercial production of organic carbonates. Much effort has been dedicated to develop the technologies for producing organic carbonates.
Take the production of dimethyl carbonate (DMC) for example. DMC is the lowest homologue of the family of dialkyl carbonates and is used widely in various organic syntheses. Traditionally DMC is industrially produced by the phosgenation of methanol. This method is gradually phased out due to the toxicity of phosgene and the need for corrosion resistant reactors.
There are two other commercialized technologies for producing DMC. One is the oxidative carbonylation of methanol using cuprous chloride as catalyst in a slurry reaction system, which is disclosed in EP 0 460 735 A2. However, the low per-pass conversion and difficult separation of catalyst from the product have been major problems requiring solution. The other one is a vapor-phase process using palladium catalyst and methyl nitrite promoter, which is disclosed in EP 0 742 198 A2 and EP 0 505 374 B1. Although the method is more promising, it involves the use of two separate reactors with two separate reaction schemes.
Besides the above-mentioned technologies being industrially exploited, many other alternative processes have been proposed recently. One of them is the alcoholysis of urea to dimethyl carbonate. In this process, in the presence of catalyst, methanol first reacts with urea producing methyl carbonate (MC), then MC formed further reacts with methanol to form target product, DMC.
The appropriate catalyst is crucial in the conversion from MC to DMC. Organotin compounds or its combination with co-catalysts are proposed in WO9,517,369, U.S. Pat. Nos. 5,565,603 and 6,010,976. The major disadvantages of this kind of catalysts are their high price and the difficult separation of the catalysts from the products. In addition, the preparation of this kind of catalysts is more troublesome. Other catalysts such as K2CO3, CH3ONa etc. are disclosed in U.S. Pat. No. 5,534,649, and ZnO in “Synthesis of Dimethyl Carbonate from Urea and Methanol over ZnO” by Wang MH et al, MCR, vol 44 7596-7599, 2005, and CaO in “Synthesis of Dimethyl Carbonate from Urea and Methanol over Solid Base Catalysts” by the same author, Catal Commun, vol 7, pp 6-10, 2006. But the DMC yields with these catalysts are low.
Thus the object of this present invention is to provide a catalyst for synthesizing organic carbonates which is prepared easily, and brings high yield and gives no pollution to the environments, and further objects are to provide the process to prepare such catalyst and the application of the catalyst in the production of organic carbonates.